The present invention relates to a light source and a laser image forming device which uses the light source.
The outline constitution of a conventional laser image forming device is shown in FIG. 22.
The conventional laser image forming device 100 is intended to project a two-dimensional picture on a screen 158. The device 100 includes laser light sources 151a-151c, an expander optical system 152, an integrator optical system 153, collection lenses 159a-159c, mirrors 161a and 161c, field lenses 154a-154c, spatial optical modulators 155a-155c, a dichroic prism 156, and a projection lens 157.
Next, an operation of the conventional laser image forming device is described.
The lights respectively emitted from the laser light sources 151a-151c of RGB three colors (R: red, G: green, and B: blue) are subjected to light expansion by the expander optical system 152, respectively. In order to make the expanded lights of RGB three colors uniformly irradiated to the spatial optical modulator 155, those RGB three colors are subjected to beam formation by the integrator optical system 153 which comprises a lens and a small lens array. The respective RGB three colors which have been subjected to beam formation are subjected to intensity modulation dependent on the respective input image signals by spatial optical modulators, and then synthesized with together by the dichroic prism 156. The intensity modulated and synthesized lights are enlarged by the projection lens 157 and, displayed on the screen 158 as a two-dimensional image. With the laser image forming device of such construction, since the lights of respective RGB light sources are monochromatic, high color purity and vivid image display is enabled by using appropriate wavelength laser sources.
By the way, with such conventional laser image forming device, in order to realize a beautiful picture in a good white balance for a long period of time, a method that can realize lengthening of a lifetime of a laser light source, stabilization of power, and can keep the power balance in the light outputs of RGB lasers constant is required.
Therefore, in the conventional method of controlling a semiconductor laser, as described in patent document 1, patent document 2, and patent document 3, it is proposed to combine the constant optical power output control (called as automatic power control: APC) and constant current control (called as automatic current control: ACC) to provide a method that can prevent the destruction of the semiconductor laser and lengthen the lifetime of the semiconductor laser.
Moreover, a method of constituting a laser light source of one color by plural laser sources and operating the same below normal power, thereby attempting lengthening the lifetime (patent document 4), and a method of interrupting a current injection for faulted light sources and taking a light output balance by using remaining laser light sources (patent documents 5) are proposed.
Furthermore, as disclosed in patent document 6, a method of detecting a long-term output reduction and lowering the set value of the output control means thereby to increase the lifetime of the semiconductor laser is proposed.
[Patent document 1] Japanese published patent application Hei. 10-178229
[Patent document 2] Japanese published patent application Hei. 10-178230
[Patent document 3] Japanese published patent application 2000-349390
[Patent document 4] Japanese published patent application 2004-214225
[Patent document 5] Japanese published patent application 2004-279943
[Patent document 6] Japanese published patent application 2002-319734